1. Technical Field
The present invention relates to a radio communication system, a receiver, and a transmitter, which are capable of reducing an operation time period of a reception circuit of the receiver and achieving reduction in power consumption in the receiver when, in the radio communication system, the receiver, such as a mobile phone, receives a synchronization signal transmitted from the transmitter, such as a base station device, and synchronizes a reference clock of the receiver with a reference clock of the transmitter.
2. Background Art
FIG. 9 is a diagram illustrating an example of configurations of a conventional transmitter and a conventional receiver which perform communication by using TDMA radio frames.
In FIG. 9, a transmitter 101C includes a radio circuit 102 for transmitting a radio signal via an antenna 103, and a transmission data control section 111C. The transmission data control section 111C includes a synchronization signal generation section 112C for creating a synchronization signal, and also has transmission data 113 stored therein. Based on the synchronization signal generated by the synchronization signal generation section 112C and the transmission data 113, a transmission signal generation section 114 generates a transmission signal to be transmitted using a radio frame. The transmission signal generated by the transmission signal generation section 114 is transmitted from the radio circuit 102 to a receiver 201C via the antenna 103.
The receiver 201C includes a radio circuit 202 for receiving the radio signal via an antenna 203, a data reception section 211C, a clock error correction section 213, and a reception operation control section 214. A synchronization signal detection section 212 of the data reception section 211C detects the synchronization signal in the radio frame transmitted from the transmitter 101C, and, based on the synchronization signal detected by the synchronization signal detection section 212, the clock error correction section 213 performs correction so that a reference clock of the receiver 201C is synchronized with a reference clock of the transmitter 101C. Based on the corrected reference clock, the reception operation control section 214 controls a data reception operation performed by the data reception section 211C.
Further, FIG. 10 is a diagram for describing a clock correction operation performed by the conventional transmitter and the conventional receiver illustrated in FIG. 9. As illustrated in FIG. 10, the transmitter 101C regularly transmits the radio frame (basic frame), and, in a leading portion thereof, the synchronization signal is transmitted.
Meanwhile, an error occurs between the reference clocks counted in the transmitter 101C and the receiver 201C, respectively. Further, this clock error increases with a lapse of time. For this reason, the receiver 201C performs a search for the synchronization signal regularly (for example, at intervals of 15 seconds), to thereby make the reference clock of its own constantly in synchronization with the reference clock of the transmitter 101C.
In the case where the receiver 2010 receives the synchronization signal, an error occurs between the reference clocks counted in the transmitter 101C and the receiver 201C, respectively, and hence, in order to receive the synchronization signal, the receiver 201C needs to start a reception operation earlier by a time period corresponding to a clock error (±Tm), which is an operation guarantee period, that is, by a time period Tm, to thereby achieve synchronization. Accordingly, in the receiver, an extended reception time period is required in order to achieve synchronization with the clock of the transmitter. This has prevented the receiver from reducing its power consumption, and it has been desired that this problem be solved.
It is noted that, as a prior art, there is disclosed a polling system in mobile radio communication (see Patent Literature 1). This polling system has an object to provide such a polling system that is capable of decreasing the probability of occurrence of a malfunction without any need to extend a time period required for the polling compared to a conventional system, and that, even if a malfunction has occurred, is capable of keeping the malfunction from adversely affecting the next time slot. Thus, such a polling system is not intended to solve the above-mentioned problem that extra power consumption is required in order to achieve the clock synchronization in the receiver.